Analysis of Crack Growth Conditions in WWER Internals Undergone High Neutron Irradiation

Conditions of stable and unstable crack growth by the mechanism of ductile fracture under quasi-static loading are analyzed. Simulation of crack growth by the finite element method (FEM) based on the strain fracture criterion was carried out. The effect of ratio of an elementary crack extension size to a plastic zone size on the kind of JR-curves is investigated. Based on these investigations conditions are determined under which unstable crack growth is possible for small scale and large scale yielding. The criterion is formulated for the absence of unstable crack growth in highly irradiated austenitic materials including the situation when the Feγ→Feα transition happens.

The Engineering Approach to Estimation of Ductile Crack Growth Under Nonisothermal Loading

The approaches to estimation of ductile crack growth under nonisothermal thermal-stress loading are considered in the paper. It is shown that in a number of cases when using isothermal JR-curves an estimation of ductile crack growth can be nonconservative. The engineering approach is proposed to estimate the value of ductile crack growth with regard to an actual history of nonisothermal thermal-stress loading. The paper cites an example of construction of nonisothermal JR-curves for the material of anticorrosive cladding of reactor pressure vessel (PVR) of WWER. Prediction of nonisothermal JR-curves by the use of finite element method (FEM) is made. It is shown that the nonisothermal JR-curves obtained by FEM and the proposed engineering approach are of a similar nature.

Analytical Determination of Material JR and Fracture Toughness Transition Curves Using Micro-Mechanical Modelling

Local approach has been used to compute a) Jinitiation and JR curves at different temperatures and b) fracture toughness transition curves for German Reactor Pressure Vessel Steel 22NiMoCr37. Ductile fracture has been analyzed using Gurson material constitutive model and probability of cleavage failure is calculated using Beremin’s model. A variation of Gurson parameter q2 near crack tip region as a function of charpy energy is suggested to obtain Jinitiation as well as complete JR curve accurately at different metal temperatures.

Influence of Constraint on JR Curves and on Maximum Load of Circumferentially Surface-Cracked Pipes

Assessment of the maximum load of circumferentially surface-cracked pipes is usually performed on the basis of JR curves measured in experimental arrangement with high constraint of plastic flow in the crack tip region, i.e. on the basis of JR curves determined conservatively. For lowering the conservatism, it is necessary to use JR curve corresponding to conditions in the pipe. Correlation between JR curves and parameter B/√a is proposed; here B is biaxiality factor defined by Leevers and Radon and a is (initial) crack length. This parameter depends on geometry only and represents — up to a numerical factor — T-stress normalized by the stress intensity factor KI. Determination of the maximum load of circumferentially surface-cracked pipes is based on JR curves corresponding to the constraint in the pipe and on the Failure Assessment Diagram defined in the R6 method. Size of the effect depends on the pipe and crack geometry (including size) and on mechanical and fracture properties of the material (including constraint dependency of JR curves). Numerical examples use published data concerning properties of steels A533B and HY-100.

Flaw Stability in Mild Steel Tanks in the Upper-Shelf Ductile Range—Part I: Mechanical Properties

Mechanical properties of 1950’s vintage, A285 Grade B carbon steels have been compiled for elastic-plastic fracture mechanics analysis of storage tanks (Lam and Sindelar, 2000). The properties are from standard Charpy V-notch (CVN), 0.4T planform compact tension (C(T)), and tensile (T) specimens machined from archival steel from large water piping. The piping and storage tanks were constructed in the 1950s from semi-killed, hot-rolled carbon steel plate specified as A285 Grade B. Evaluation of potential aging mechanisms at both service conditions shows no loss in fracture resistance of the steel in either case. Site and literature data show that the A285, Grade B steel, at and above approximately 70°F (21°C), is in the upper transition to upper shelf region for absorbed energy and is not subject to cleavage cracking or a brittle fracture mode. Furthermore, the tank sidewalls are 1/2 or 5/8-in. (12.7 or 15.875 mm) thick, and therefore, the J-resistance JR curve that characterizes material resistance to stable crack extension under elastic-plastic deformation best defines the material fracture toughness. The JR, curves for several heats of A285, Grade B steel tested at 40°F (4.4°C), a temperature near the average ductile-to-brittle (DBTT) transition temperature (CVN at 15 ft-lb or 20.3 J), are presented. This data is applicable to evaluate flaw stability of the storage tanks that are operated above 70°F (21°C) since, even at 40°F (4.4°C), crack advance is observed to proceed by ductile tearing. [S0094-9930(00)00402-9]